1. Field of the Invention
The present invention relates in general to a driving device and a driving method for a flat panel display. In particular, the present invention relates to a driving device and a driving method to decrease the switching frequency of a data chip, which provides the addressing voltage of the data electrodes of a flat panel display, by changing the scanning order of the scanning electrodes.
2. Description of the Related Art
Flat panel display comprises liquid crystal display (LCD), organic light-emitting display (OLED), and plasma display panel (PDP), etc. The advantages of the plasma display panel are small size, good display performance, and high reliability. Thus, PDP is often used in current electric equipment.
The current method of driving a plasma display panel is achieved through a plurality of subfield-display operations, which altogether constitute a full frame-display operation. For example, a picture frame in a plasma display panel with 256 gray levels may comprise eight subfields SF0xcx9cSF7 as shown in FIG. 1A. Each subfield-display operation comprises steps of resetting, addressing, and sustaining the display signal. Specifically, a plasma display panel is driven by a driving signal which comprises an erasing period, a addressing period, and a sustaining period. During the erasing period, residual ions of each illuminant cell of a PDP are erased using a voltage pulse having a pulse width shorter than a sustaining pulse. During the addressing period, external data are input using a voltage pulse having a voltage higher than a sustaining pulse of the erasing period. During the sustaining period, an AC voltage of a constant frequency is applied to avoid an ignition miss or incorrect display and to obtain a correct power margin.
FIG. 1B shows a cross section of a conventional PDP structure, and FIG. 1C shows a schematic top view of the data and scanning electrodes of the same PDP. As shown in FIG. 1B, a PDP is constructed by joining a front glass substrate 1 with a rear glass substrate 2, wherein data electrodes 3 for inputting external data are formed on the surface of the front glass substrate 1 that opposes the rear glass substrate 1. Furthermore, a plurality of ribs 4 is defined on the data electrodes 3 to form illuminant cells. A plurality of sustaining electrodes 7 and scanning electrodes 8 in parallel direction, on the other hand, are formed on the surface of the rear glass substrate 2 that opposes the front glass substrate 1, wherein the above-mentioned data electrodes 3 are formed perpendicular to both the sustaining electrodes 7 and the scanning electrodes 8.
In addition, the surfaces of both the sustaining electrodes 7 and scanning electrodes 8 are coated with a dielectric layer 6 (such as a MgO layer) for protecting the surfaces of the electrodes. Furthermore, a fluorescent material 5 (such as phosphorous) is deposited between ribs (where the illuminant cells reside) for illumination to occur as soon as a voltage is applied. As shown in FIGS. 1C and 1D, a typical conventional plasma display panel comprises a plurality of row plasma display units (represented by L1xcx9cLN). Each row display unit has one of the plurality sustaining electrodes 7 (represented by a corresponding X1xcx9cXN), one of the plurality of parallel scanning electrodes 8 (Y1xcx9cYN); for example, the first row display unit L1 comprises the first sustaining electrode X1, and the first scanning electrode Y1. The plurality of illuminant cells of the first row display unit L1 is driven by the X1, Y1 simultaneously during the sustaining period. The plurality of data electrodes 3 (A1xcx9cAM) are disposed perpendicular to both the sustaining electrodes 7 (X1xcx9cXN) and the scanning electrodes 8 (Y1xcx9cYN). Each of the sustaining electrodes 7 (X1xcx9cXN) is connected to the others and thereby the electrodes can be driven synchronously. In contrast, each of the scanning electrodes 8 (Y1xcx9cYN) is separately connected from the other electrodes so as to actuate each of the electrodes independently. Thus, external data are input to each illuminant cell of the plasma display panel via the data electrodes 3 (D1xcx9cDM) by controlling both the sustaining electrodes 7 (X1xcx9cXN) and the scanning electrodes 8 (Y1xcx9cYN).
FIG. 2 is a driving signal diagram of various electrodes of the plasma display panel shown in FIGS. 1B, 1C, and ID, which are driven according to the method of a prior art. Accordingly, a plasma display panel is driven by a driving signal comprising an erasing period, an addressing period, and a sustaining period. During the erasing period, a very short pulse VW of a high voltage is applied to all of the sustaining electrodes 7 (including X1xcx9cXN), and all of the scanning electrodes 8 (including Y1xcx9cYN) are connected to the ground Vg, so as to remove the remaining residual ions. At this point, no data electrodes 3 (including D1xcx9cDM) are yet driven. During the addressing period, a bias VK is applied to all of the sustaining electrodes 7 (including X1xcx9cXN), so the scanning electrodes 8 (Y1xcx9cYN) can input external data sequentially via the data electrodes 3 (D1xcx9cDM) based on an addressing signal VY. At this point, the scanning electrodes 8 (Y1xcx9cYN) are connected to a row address decoder (not shown in the figure) to receive an addressing signal, and the data electrodes 3 (D1xcx9cDM) are connected to external data to precede write operations. During the sustaining period, a periodic voltage pulse Vs is alternately applied to the sustaining electrodes 7 (X1xcx9cXN) and the scanning electrodes 8 (including Y1xcx9cYN) to maintain the luminance of the illuminant cells.
During the addressing period, conventional method enables the scanning electrodes according to the subfield data in a fixed order, and the data chip provides the addressing voltage to the data electrodes corresponding to the driven scanning electrodes. However, the number of the switching cell of the data chip is directly proportional to the used power, because there is a parasitical capacitor Cd between the electrodes. When the voltage between the electrodes is raised to Vdd, the consumed power is (xc2xd)CdVdd2. Moreover, when the voltage between the electrodes returns to a low level, the consumed power is (xc2xd)CdVdd2 again. The consumed power increases the temperature of the data chip, especially when the subfield data is interleaved scanning, and the temperature may reaches 100xc2x0 C., which wastes power and decreases the life of the data chip.
The object of the present invention is to provide a driving device and a driving method for a flat panel display, which analyzes the characteristic of the subfield before addressing, and addresses the electrodes in a suitable order to decrease the voltage switching frequency of the data chip.
Moreover, another object of the present invention is to provide a driving device and a driving method for a flat panel display, which detects the output current of the power supply to the flat panel display. When the output current exceeds a predetermined value, the scanning order of the flat panel display is changed to decrease the output current, such that the voltage switching frequency of the data chip is decreased.
To achieve the above-mentioned object, the present invention provides a driving method for a flat panel display. First, an image signal is transformed to frame data. Next, a characteristic data of the frame data is obtained. Next, a scanning order of the first electrodes is determined according to the characteristic data. Next, scanning electrodes are driven in the scanning order during the addressing period. Finally, the data electrodes corresponding to the first electrodes are driven to perform the addressing operation.
Moreover, the present invention provides a driving method for a flat panel display comprising a power supply, first electrodes, and second electrodes corresponding to the first electrodes. The driving method comprises the steps of driving the first electrodes and corresponding second electrodes in a first scanning order during the addressing period to perform the addressing operation, detecting the current output from the power supply, and driving the first electrodes and corresponding second electrodes in a second scanning order different from the first scanning order when the current output from the power supply is larger than a predetermined value for a predetermined time.